reegle

A SELECT query e.g. consists of binding variables and a set of triple patterns in the WHERE-clause. Here is a simple SELECT query that selects the names of an actor:

SELECT ?actorName
WHERE {
  <http://reegle.info/actors/2354> <http://xmlns.com/foaf/0.1/name> ?actorName.
}

In our data set the triple pattern from above will match two triples:

If you run this query against the SPARQL endpoint of reegle you will get two results - namely: the english and local name of the actor with the URI http://reegle.info/actors/2354.

Let's now assume we are only interested in the english name of the actor. We can get that information by including a basic FILTER expression in our query:

SELECT ?actorName
WHERE {
  <http://reegle.info/actors/2354> <http://xmlns.com/foaf/0.1/name> ?actorName.
  FILTER (lang(?actorName) = "en")
}

This will filter out all labels that have no language tag "en" attached to them and leave you just with the english name:

To strip the redundant namespace information from URIs in your SPARQL query you can use prefixes as in most of RDF serialization formats

So in the simple query from above the foaf namespace can be replaced using a PREFIX declaration at the beginning of the query:

PREFIX foaf:<http://xmlns.com/foaf/0.1/>
SELECT ?actorName
WHERE {
  <http://reegle.info/actors/2354> foaf:name ?actorName.
}

Below are a couple of more advanced example queries you can try using the reegle SPARQL endpoint.

Retrieve all categories and their labels from the data set:

PREFIX skos: <http://www.w3.org/2004/02/skos/core#>

SELECT DISTINCT ?category ?categoryLabel
WHERE {
  ?category a skos:Concept.
  ?category skos:prefLabel ?categoryLabel.
}

Select all actors that are active in portugal and in the category "Research/University":

PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX dcterms: <http://purl.org/dc/terms/>
PREFIX reegle: <http://reegle.info/schema#>

SELECT ?actor ?name 
WHERE {
  ?actor a foaf:Organization.
  ?actor dcterms:subject <http://reegle.info/categories/12>.
  ?actor foaf:name ?name. FILTER (lang(?name) = "en" )
  ?actor reegle:activeIn <http://reegle.info/countries/PT>.
}

Retrieve all specialisations and their titles:

PREFIX reegle: <http://reegle.info/schema#>
PREFIX dc: <http://purl.org/dc/elements/1.1/>

SELECT DISTINCT ?specialisation ?specTitle
WHERE {
  ?specialisation a reegle:Specialisation.
  ?specialisation dc:title ?specTitle.
}

Select the number of project reports for the specialisation "Policy and Regulation" ordered by country:

PREFIX dbprop: <http://dbpedia.org/property/>
PREFIX reegle: <http://reegle.info/schema#>
PREFIX geonames: <http://www.geonames.org/ontology#>

SELECT ?countryName count(?country) as ?count 
WHERE {
  ?project a reegle:ProjectOutput.
  ?project reegle:specialisation <http://reegle.info/specialisations/34>.
  ?project dbprop:country ?country.
  ?country geonames:name ?countryName.
} 
ORDER BY DESC(?count)

Note: The underlying SPARQL endpoint is provided by OpenLink Virtuoso, therefore you can use things like COUNT in your SPARQL queries even though it is not supported in the current official SPARQL specification.

You can use the SPARQL endpoint as a web service simply by sending a HTTP POST request to the endpoint URL and provide the following parameters (URL-encoded):

• query - the SPARQL query string
• format - specifies the result format

For SELECT queries the available formats are:

• application/sparql-results+xml
  XML serialisation
• application/sparql-results+json
  JSON serialisation
• text/html
  HTML table
• application/javascript
  Javascript
• text/plain
  NTriples
• application/rdf+xml
  RDF/XML
• application/vnd.ms-excel
  Excel Spreadsheet

For CONSTRUCT and DESCRIBE queries (returning triples) the available formats are:

• text/rdf+n3
  Notation 3
• application/rdf+xml
  RDF/XML
• text/plain
  NTriples
• application/xhtml+xml
  HTML + RDFa
• application/rdf+json
  RDF as JSON